This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to European Patent Application No. 99 101 595.9 filed in Europe on Jan. 29, 1999 and European Patent Application No. 00 100 242.7 filed in Europe on Jan. 18, 2000; the entire content of which is hereby incorporated by reference.
The present invention relates to a method for the optimization of a copying light profile of a photographic copier. The present application especially relates to the optimization of a copying light profile in a copier, which includes a local transmission modulator, for example a liquid crystal matrix. The invention further relates to the use of such a local transmission modulator in a photographic copier for the achievement of optimization.
Copier apparatuses for the copying of photographic originals, especially transparent originals, for example films (positive films, negative films), are known, for example, from DE 4308864, DE 4040498, or DE 19703063. The copier apparatuses described therein use an LC matrix (liquid crystal matrix) in order to influence the copying light used for the exposure process. The LC matrix serves the brightening or darkening of certain regions of the copy in order to so manipulate the copy of a photographic original in a desired manner. The mask used therefor according to which an LC matrix is controlled is derived from the photographic original and is therefore dependent on its respective image data.
Optical components such as a high-value illumination means and optical, light guide means, for example, mirrors, elliptical mirrors, lenses, stops, filters, light mixers, shutters and so on are used in a copier apparatus in order to achieve as smooth a profile as possible of the copying light (which means the copying light intensity or the copying light density) which is as free from variations as possible in order to thereby illuminate the original as optimally as possible.
However, in practice, the copying light profile achieved is not optimal. This can be caused, for example, by a less than optimal cooperation of the light conducting means or by undesired modifications of the copying light by the light conducting means. For example, annular structures can occur.
The inventors of the present application have realized that a local transmission modulator, for example an LC matrix or a controllable scatter matrix, can be used during a respective copier process not only for the manipulation of a copy in dependence of a given original, but also for the general improvement of the copying properties of a specific copier, and independent from the original to be respectively copied.
It is an object of the invention to provide a method and apparatus by which the copying light profile in a copy apparatus can be optimized. Furthermore, in accordance with the invention a local transmission modulator is used for this optimization.
Advantageously, a cost-effective optimization of the copying light profile is possible by using a local transmission modulator already present in a copier apparatus. The costly optimization process for then calibration of the optical components can then be simplified. It is further made possible to use cheaper optical components with larger manufacturing tolerances, since inhomogentities caused thereby can be equalized with the method in accordance with invention.
The method in accordance with invention is used in a photographic copier as described, for example, in European application number 99101595.9 and corresponding application s in USA, Japan, Canada and China, the disclosure of which is here by incorporated into the application. Such a copier apparatus uses at least one light source, for example a halogen lamp or LED diodes to produce the copying light. The produced copying light is guided in the copier apparatus through a number of optical, light conducting means, for example, shutters, lenses, mirrors, partially transparent mirrors, beam splatters, lenses, diffuses, prisms, and so on, along a beam path (optical axis) through the photographic original to the copier material. The light is preferably homogenized by homogenizing means, for example scatter disks, before it reaches the photographic original. The photographic original is transparent and can be, for example, a negative film or a positive film. The copier material is, for example, a photographic paper. The photographic original is shone through and the shone through original image is projected onto the copier material.
The copying light profile is then considered optimal when it takes on a desired form. Preferably, the copying light profile is formed in such a way (in the plane of the copy) that the copy of a photographic original results in a homogeneous copy (for example, homogeneously gray) when the photographic original is based on the photographic recording (for example by way of a camera) of a homogeneous (for example, homogeneously gray) image. If the photographic recording were perfect, the photographic original would then also be homogeneous and one would therefore desire a homogeneous copying light profile. However, the recording lenses of cameras cause a decrease of the exposure light strength from the center to the edge. Therefore, a copying light profile is then preferably considered optimal, when it at least partly equalizes this decrease and not only attenuates disruptions of the copying light caused by the light conducting means. A homogeneous picture recorded by a camera is thereby duplicated by an at least approximately homogeneous copy.
A local transmission modulator is preferably positioned in a photographic copier apparatus in the vicinity of the original and either therebefore or thereafter. The copying light is passed through the local transmission modulator. The local transmission modulator can change its transmission whereby it is preferably electrically controlled therefor. The change of the transmission preferably takes place spacially broken down (locally), which means different transmissions can be adjusted at different locations (elements of the transmission modulator). As already described in connection with the prior art, a specific transmission profile is adjusted at the transmission modulator in order to manipulate the brightness profile of the copy depending on the image data of the original for the copying of a photographic original. This transmission profile is in the following referred to as transmission profile preselected for the copying process. If no manipulation of the copy is planned, an even transmission profile is preselected according to the prior art. This was then the case in the prior art, for example, when the photographic original was a homogeneous picture.
According to the process in accordance with invention, the transmission profile of the local transmission modulator preselected for the copy process is changed in dependence of a given (actual) and a desired (nominal) copying light profile. The copying light profile can be described, for example, as the profile of a copying light intensity or an optical density of the copying light or the illumination intensity of the copying light or as the function of these variables. The transmission profile during the copying of an original which is supposed to represent a homogeneous picture is changed in such a way that inhomogeneities in the copy are removed or at least attenuated.
To change a transmission profile in such a way that the copying light profile is optimized, several steps are required. First, the given copying light profile in a copier apparatus must be measured. This copying light profile is dependent of the optical components used (light source; light conducting means; light scattering means, such as LC matrix, scatter disks; means light absorbing means, such as filters or also LC matrix) and depending on the type of the copier apparatus can even vary from copier to copier of the same type. The copying light profile broken down per area describes the strength of the copying light transverse to the light path in the copy plane (for example, expressed as intensity or optical density). In order to measure this, essentially two steps are required. A defined measuring environment for the measuring of the copying light profile is created in a first step. For this purpose a transparent element with a known transmission profile is preferably entered into the light path instead of any arbitrary photographic original. This can be, for example, a test filter, the spectral transparency of which is adapted to the spectrum of an average original. Preferably, the transparent element is positioned between original and copy plane, especially preferably in the vicinity of the projection lens, for example, in the stop plane of the projection lens or directly under the projection lens. Also possible is a placement of the transparent element at the location where during the normal copier operations (but not during the measuring of the copying light profile), the photographic original is located, or in the vicinity of that location. The transparent element can be a photographic original exposed in an appropriate manner which has especially a smooth or homogeneous transmission profile. It can also be a photographic original which was produced by the photographic recording of a homogeneously gray image and has the typical edge decline of the transmission as occurs in pictures made with a typical camera. In this case, the desired nominal profile in the copy plane is then homogeneous. The desired copying light profile (nominal profile) is preferably independent of the image content of the photographic originals to be copied.
The transparent element can also be, for example, a gray filter. Alternatively, no transparent element or a completely transparent element can be provided in the light path. In this alternative case, only a short measurement period is used for the measurement of the copying light profile.
Before the optimization process, a transmission profile specific for the local transmission modulator is preferably provided for the further assessment of the measurement environment. The transmission characteristics which depend on the control variables (control voltages) are known for each transmission element of the local transmission modulator. The transmission profile specific for the measurement is preferably smooth or homogeneous.
If, as described above, a defined measurement environment is created for the measurement of the copying light profile, whereby, contrary to the copying process, no photographic original (of unknown transmission) is located in the light path of the copier apparatus, the copier light is measured in a subsequent step for the determination of the copying light profile. This measurement preferably takes place after the copying light has passed the transparent element or after the last optical components (for example, the last light conducting means). Especially preferred is the measurement of the copying light profile in the copy plane or in the vicinity of the copy plane. For example, a conventional copier material (photographic paper) can be fastened in the copy plane and the exposed copier material then examined for brightness variations, whereby the grading of the copier material must be considered. The exposed copier material can therefor be scanned, for example, by a scanner or densitometer with preferably calibrated gray scale, in order to thereby digitalize the copying light profile measured with the copier material (photographic paper). Alternatively, other light detection means broken down by area, for example, a diode array for the measuring of the copying light profile can be used. Such a detector for the measurement of the copying light profile can be positioned, for example, in the copy plane or in the vicinity thereof so that it does not interfere with the normal copier operation (for example, rotated in) or the copy plane can for this measurement step be projected onto a copying light detector by way of a projection optic or by way of a mirror.
If the copying light profile is determined in the manner described above and especially when digitalized, the transmission profile of the local transmission modulator can be changed based on the profile determined (for example intensity profile, profile of the optical density). For example, if it has been determined that certain areas in the copying light profile are undesirably brighter than the remaining areas, the transmission profile of the local transmission modulator is locally reduced in such a way that those brighter areas are darkened to the brightness of the remaining areas. For the case of a liquid crystal matrix, the transmission of the liquid crystal elements associated with this area is thus lowered in an appropriate manner. In the case of a photographic paper, bright areas of the copying light profile result in darkened areas on the photographic paper.
In order to optimize tie copying light profile for the copying process of photographic originals, the transmission profile preselected for the copying process is preferably changed so that a copy results which corresponds to a copy that would have been achieved with a copier with an optimum copying light profile. The transmission profile preselected for the copying process is therefor-preferably changed so that one would have detected an optimum copying; light profile with a corresponding change of the specific transmission profile used for the measurement of the copying light profile. The optimization is such that one determines upon a further determination of the copying light profile that the deviation of the determined copying light profile from the desired copying light profile is smaller or minimized. Such a repeated determination or measurement can be carried out in order to test the optimization. However, this is not absolutely necessary. Also, an iterative approximation to the optimum results can be achieved with several determination or measurement processes and changes of the transmission profile based thereon. The local transmission modulator is thereby preferably controlled so that a focused projection of the transmission modulator onto the copy plane results. However, one refrains from an iterative approximation upon an unfocused projection of the local transmission modulator onto the copy plane.
In order to achieve the desired copying light profile, preferably a mathematical relationship is determined between the desired copying light profile and the determined (measured) copying light profile and/or the deviation or difference between the desired and the determined copying light profile and, based thereon, the transmission profile of the local transmission modulator preselected for a copier process is changed.
For example, if a region (element) 1 of the local transmission modulator upon focused projection is associated on the basis of the optical projection geometry present with a region ixe2x80x2 in the copy plane, and if the local transmission modulator in the region (element) i has a specific transmission Ti (before the optimization) then the copying light profile is expressed in the region i I in the copy plane, for example, by an intensity Ii, of the copier light. For this case, the transmission of the local transmission modulator Ti is then preferably changed to an optimal transmission Topti. Thus, upon expression in transmission and intensity, it results:
Topti=Tixc3x97(Inomi, Ii,)
Ii, is thereby the measured intensity at the location ixe2x80x2, Inomi, the nominal intensity at the location ixe2x80x2, Ti the transmission of the element 1 of the transmission modulator and Topti, the optimized transmission of the element i.
The transmission matrix of the local transmission modulator is preferably projected out of focus onto the copy plane for the copying of an original, in order not to make visible any sharp brightness edges in the copy. However, for the measurement of the copying light profile it is preferably projected in focus. The transmission modulator can therefor be designed for variation between a focused and an unfocused position.
Preferably, a copying light profile once measured and determined is used for the change of the transmission profile during a plurality of copying processes, especially with different photographic originals.
It is advantageous to measure the copying light profile after the copying light has passed at least the multitude of the optical components (light scattering, light of sorting and light conductive means), in order to so detect the essential inhomogeneities or copy errors during the copying light measurement. Especially preferably, the copying light measurement is carried out after passage through a local transmission modulator. Especially those inhomogeneities caused by the local transmission modulator can thereby be taken into consideration.
If in a copier, for example depending on the original or a film type, a different spectral composition of the copying light (copying light of different colors) is used or if a sequential exposure with different colors has taken place, the copying light profile is preferably determined for the respectively used copying light (of one specific color) and the, change of the transmission profile of the local transmission modulator carried out depending on the spectral composition (color) of the copying light. When within a copying process, i.e. during the projection of an original onto a copier material, copier light of different spectral composition (color) is sequentially used, the transmission profile of the local transmission modulator is preferably changed in the corresponding time sequence depending on the spectral composition (color) of the copying light, and especially according to the copying light profile measured for each copying light (of a specific color).
Preferably, a compensation matrix is determined from the determined copying light profile (see also FIG. 2), which is stored and used for the change of the transmission profile during each copying process. The change of the transmission profile is preferably based on a digital calculation process. A transmission matrix describing the transmission profile is thereby preferably calculated based on the compensation matrix mentioned. The copy matrix specific for each copying process thereby enters into the calculation of the transmission matrix. The copy matrix is especially determined from the image data of the photographic original in that, for example, the photographic original is optically detected or scanned before the copying process. If the elements of the copy matrix and the compensation matrix respectively describe optical densities, the transmission matrix then results, for example, simply by addition of the copy matrix and the compensation matrix.
When different projection lenses are used in a copier corresponding to different enlargements, a compensation matrix can be stored for each projection lens and can then be applied according to the projection lens respectively used. This is especially advantageous because different lenses have a different decline of the copying light intensity from the center to the edge. An optimal copying light can thereby be achieved for each desired enlargement (projection lens).
A transparent element for the measurement of the copy or light profile, for example, a gray filter or a suitably exposed photographic original can be permanently provided in a photographic copier in accordance with invention. The transparent element can then be moved, for example, for the measurement into the light path (for example, rotated thereinto) and is preferably removed from the light path for the conventional copying processes. Conversely, any photographic original of unknown transmission profile, for example, a normal original to be copied is preferably removed from the light path for the measurement of the copying light profile. Also, a light measuring device such as, for example, a photo diode array can be permanently provided in the copier for the measurement of the copying light profile. This measuring device can be positioned, for example, in the paper platform. The transparent element is preferably so mounted that it can be automatically inserted into the light path when a measurement of the copying light profile is to be carried out. On desired changes of the copying light profile can be detected in this manner for example, in certain operating time intervals and compensated. Also, an input device can be provided for the input of a compensation matrix by a maintenance person who has measured the copying light profile and calculated the compensation matrix there from.